Photonically engineered incandescent emitter

ABSTRACT

A photonically engineered incandescence is disclosed. The emitter materials and photonic crystal structure can be chosen to modify or suppress thermal radiation above a cutoff wavelength, causing the emitter to selectively emit in the visible and near-infrared portions of the spectrum. An efficient incandescent lamp is enabled thereby. A method for fabricating a three-dimensional photonic crystal of a structural material, suitable for the incandescent emitter, is also disclosed.

STATEMENT OF GOVERNMENT INTEREST

[0001] This invention was made with Government support under contractno. DE-AC04-94AL85000 awarded by the U.S. Department of Energy to SandiaCorporation. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to incandescent lamps, and moreparticularly to incandescent lamps made from photonically engineeredthermal emitters.

[0003] Incandescent lamps offer very high quality lighting, areinexpensive, and are the most popular lighting technology forresidential use. They are also, unfortunately, the least efficient(energy to useful light) lighting technology used commercially today. Anexcellent overview of incandescent lamp technology is given in Bergmanet al., Filament Lamps, GE Research and Development Center, Report98CRD027, February 1998.

[0004] The lighting industry commonly uses the term luminous efficacy todescribe the efficiency of a lamp. Luminous efficacy is frequentlydefined as the luminous flux divided by the total radiant power in unitsof lumens/Watt. The luminous flux has units of lumens, and is theradiant flux weighted by the human eye response. A better descriptionfor the efficiency of a lamp is to divide the luminous flux by the totalinput power to the lighting source, so that the electrical performancecan be factored into the comparison of lighting technologies. Thisdisclosure will use the latter definition for luminous efficacy, sincesome lighting approaches have inherently less efficiency in convertinginput electrical power into radiant power.

[0005] The luminous efficacy of a 60W incandescent lamp using a tungstenfilament is only about 15 lumens/Watt. The luminous efficacy of theincandescent lamp is low because much of the light (around 90%) isemitted by the tungsten filament in the non-visible infrared(wavelengths longer than 760 nm) portion of the spectrum. Fluorescentlamps are much more efficient than incandescent lamps, and have luminousefficacies between 75 and 100 lumens/Watt. By comparison, thetheoretical maximum luminous efficacy for high-quality white lightingusing a broad spectral source is around 200 lumens/Watt.

[0006] An incandescent lamp works by heating up a tungsten filament to asufficiently high temperature (typically around 2800° K) that itradiates in the visible portion of the electromagnetic spectrum (roughly380 to 760 nm). Such high-temperature bodies are commonly referred to as“emitters” or “radiators”. The radiation from a high-temperature emitteris described by the theory of blackbodies. An ideal blackbody emits thetheoretically maximum radiation. Real emitters do not radiate as well asan ideal blackbody. The emissivity is the ratio of the radiation from areal emitter to the radiation of an ideal blackbody, and is unitlesswith a value between 0 and 1.

[0007] The luminous efficacy of the incandescent lamp can be improved bymodifying the emissivity of the emitter. The optimum emitter forlighting purposes would have an emissivity of unity in the visibleportion of the spectrum and an emissivity of zero in the non-visibleportions of the spectrum. Such an emitter would emit all the light inthe useful visible portion of the spectrum and no light in thenon-useful non-visible portion of the spectrum. A 2800° K emitter withsuch an optimized selective emission would have a luminous efficacyapproaching 200 lumens/Watt, or over 10× improvement compared to currentincandescent lamps and 2× improvement compared to current fluorescentlamps.

[0008] There remains a need for a high-temperature emitter thatselectively emits radiation in the visible portion of the spectrum,thereby enabling an incandescent lamp having improved luminous efficacy.

SUMMARY OF THE INVENTION

[0009] The present invention provides a photonically engineeredincandescent emitter, comprising a photonic crystal having acharacteristic lattice constant and comprising an emitter materialhaving a first dielectric constant and at least one other latticematerial having at least one other dielectric constant and wherein thecharacteristic lattice constant, the emitter material, and the at leastone other lattice material are chosen so as to create a photonic bandgapthat suppresses or modifies thermal emission above a desired cutoffwavelength. The emitter material can comprise a refractory non-metal ora refractory metal, such as tungsten. The photonically engineeredincandescent emitter can thereby be tailored to selectively emit thermalradiation in the visible and near-infrared portions of the spectrum,enabling a more efficient incandescent lamp.

[0010] The present invention further provides a method for fabricatingthe photonically engineered structure, suitable for the incandescentemitter, comprising forming a lattice structure mold of a sacrificialmaterial on a substrate; depositing a structural material into thelattice structure mold; and removing the sacrificial material from thelattice structure mold. Silicon integrated circuit technology isparticularly well suited to forming the lattice structure mold to enablethe formation of photonic crystals of refractory materials with latticeconstants on the order of the wavelength of visible light.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and formpart of the specification, illustrate the present invention and,together with the description, describe the invention. In the drawings,like elements are referred to by like numbers.

[0012]FIG. 1 shows the estimated luminous efficacy of an optimizedincandescent source where the emissivity is unity above and zero below acutoff wavelength.

[0013]FIG. 2 shows a schematic illustration of a three-dimensional (3D)“Lincoln-Log” type photonic crystal structure.

[0014]FIG. 3 illustrates a fabrication sequence for a four-layerLincoln-Log type tungsten photonic crystal.

[0015]FIG. 4 shows a cross-sectional scanning electron micrograph of afour-layer tungsten photonic crystal built on a (001) oriented siliconsubstrate. FIG. 4a shows the tungsten photonic crystal prior to removalof a silica sacrificial mold. FIG. 4b shows the tungsten photoniccrystal after removal of the silica sacrificial mold. Theone-dimensional tungsten rod used to form the crystal has a rod width of1.2 μm and the rod-to-rod spacing of 4.2 μm.

[0016]FIG. 5 shows the measured reflectance and transmittance spectrafor the light propagating along the <001> axis of the four-layertungsten photonic crystal.

[0017]FIG. 6 shows the tilt-angle reflectance spectra from thefour-layer tungsten photonic crystal.

[0018]FIG. 7 shows the computed transmission spectra for tungstenphotonic crystals with N=2, 4 and 6 layers.

[0019]FIG. 8 shows the spectral emissivity of the four-layer tungstenphotonic crystal having a lattice constant of 4.2 μm.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention comprises a photonically engineeredincandescent Is emitter that is more efficient than conventionalincandescent lamps and a method for making the same. The more efficientincandescent emitter of the present invention is enabled by improvingthe emission selectivity of a high-temperature emitter usingphotonically engineered structures. Photonically engineered structuresconsist of materials with a periodic variation on the order of thewavelength of light. The periodic variation changes the allowed opticalmodes in the medium, leading to many varied and useful properties. Somephotonic structures completely eliminate optical modes in all directionsfor a specific band of wavelengths. These structures are said to exhibita three-dimensional (3D) photonic bandgap. A description of photoniccrystals and their properties is given by Joannopoulos et al., PhotonicCrystals: Molding the Flow of Light (1995).

[0021] The thermal emission spectrum and, therefore, the emissivity canbe altered by suitable modification of the properties of photonicstructures. The use of photonic structures for the control of emissionof thermal radiation from an object is disclosed in copending U.S.patent application Ser. No. 09/441,221 to Lin and Fleming, which isincorporated herein by reference. Modification of the thermal radiationfrom a photonic structure in the infrared portion of the spectrum hasbeen described by Lin et al. in “Enhancement and suppression of thermalemission by a three-dimensional photonic crystal,” Phys. Rev B62, R2243(2000). Lin et al. fabricated a 3D “Lincoln-Log” type silicon photoniccrystal with air as the second dielectric. The silicon photonic crystalhad a lattice constant of 4.2 μm and a large photonic bandgap coveringthe infrared wavelength range from λ=9-15 μm. When heated to 410° C.,the silicon photonic crystal exhibited significantly reduced emissivitybetween 10 and 16 μm, indicative of the 3D photonic band gap.

[0022]FIG. 1 shows the luminous efficacy 100 for an optimizedincandescent source having an emissivity of unity above and zero below acutoff wavelength. The luminous efficacy is maximized by moving thecutoff wavelength as close as possible to the long-wavelength edge ofvisible light (i.e., 760 nm). Luminous efficacies approach 200lumens/Watt with such an optimized emitter. Thus, for incandescentlighting applications in the visible portion of the spectrum, thephotonic bandgap of the photonic crystal must be closer to thelong-wavelength edge of visible light than was obtained with the siliconphotonic crystal of Lin et al.

[0023] To move the photonic bandgap closer to the long-wavelength edgeof visible light, the photonic crystal can have smaller dimensions anduse materials that have greater dielectric contrast and can toleratehigh temperatures (e.g., 2800° K). As described by Bergman et al., themost common material used for incandescent lamp filaments aretungsten-based materials. As a metal, tungsten also offers the advantageof a large refractive index when used in a photonic crystal. A largedifference in the refractive index enhances the effect of the periodicvariation of the refractive index on the optical modes in the photoniccrystal, thereby producing a photonic crystal with a large photonicbandgap wherein the emissivity is reduced.

Photonically Engineered Emitter Structures

[0024] The present invention discloses a 2D or 3D photonic crystal thatselectively emits at visible and near-infrared wavelengths. Varioustypes of photonic crystal structures that exhibit a 2D or 3D photonicbandgap known to those in the art are suitable for the presentinvention. Some examples of photonic crystal structures and thefabrication thereof are disclosed in U.S. patent application Ser. No.09/296,702 to Fleming and Lin, which is incorporated herein byreference.

[0025] A common type of photonic crystal exhibiting a 3D photonicbandgap that will be used as an illustrative example in the presentdisclosure is the Lincoln-Log type of photonic crystal structure 200shown schematically in FIG. 2. The 3D Lincoln-Log type structurecomprises alternating layers 210, each layer 210 further comprising anevenly spaced row of parallel “logs” or rods 220 of material with afirst dielectric constant. The spaces between the rods 220 are filled bya material 230 having a second dielectric constant. For simplicity aswell as for high dielectric contrast, material 230 is often air. For afour-layer photonic crystal 200, the one-dimensional rods 220 have astacking sequence that repeats itself every four layers with a repeatdistance of c. Within each layer 210, the axes of the rods 220 areparallel to each other with a pitch of d. Alternate layers 210 arerotated by 90 degrees relative to the previous layer. Between each layer210, the rods 220 are shifted relative to each other by 0.5 d. Theresulting structure has a face-centered-tetragonal lattice symmetry ofwhich the diamond structure is a subset. For the special case ofc/d=1.414, the crystal 200 can be derived from a face-centered-cubicunit cell with a basis of two rods.

Fabrication of the Photonic Crystal

[0026] Photonic crystal structures exhibiting 2D or 3D photonic bandgapssuitable for the present invention can be fabricated by various methodsknown to those skilled in the art. The vertical topology of the 3Dphotonic crystal structure can be built by repetitive deposition andetching of multiple dielectric films in a layer-by-layer method. Onelayer-by-layer method for fabricating the photonic crystal is to buildup the structure directly with the structural material, as was done forthe silicon photonic crystal of Lin et al., described above.Alternatively, the fabrication process can comprise forming a latticestructure mold for the structural material in a sacrificial material,selective deposition of the structural material into the latticestructure mold, and finally removing the sacrificial material from thebackfilled mold to leave a photonic crystal of the structural material.The latter method may have advantages for structural materials that canotherwise build up large residual stresses during a directlayer-by-layer fabrication process. This fabrication process can be usedto form photonic crystals of a wide variety of structural materials thatcan be deposited by a conformal process, including metals, metal alloys,and semiconductors.

[0027] For illustrative purposes, described below and illustrated inFIGS. 3a-3 i is a layer-by-layer fabrication sequence for a 3D LincolnLog tungsten photonic crystal suitable for the incandescent emitter ofthe present invention. The tungsten photonic crystal described hereinhas a pitch between adjacent rods of d=4.2 μm, a rod width of w=1.2 μm,and a layer thickness of 1.6 μm. Photonic crystals of other refractorymetals and non-metals, such as tungsten alloys, silicon carbide, carbon,and titania, are also suitable for the photonically engineeredincandescent emitter of present invention.

[0028] The lattice structure mold can be formed by sequential depositionof a cavity-forming structural material, such as polysilicon, inalternating patterned layers of a sacrificial mold material, such assilica (SiO₂). The basic layer-by-layer polysilicon in silicafabrication sequence is described by Lin et al. in Nature 394, 251(1998) and in the copending U.S. patent application Ser. No. 09/296,702to Fleming and Lin. The layer-by-layer fabrication method disclosed byFleming and Lin enables layered material composition with precisethickness, planarity, and alignment control.

[0029] In FIG. 3a, a first layer 310 comprised of the sacrificial moldmaterial, e.g., silica, is deposited onto a silicon substrate 300. Thethickness of silica layer 310 is greater than the desired thickness ofthe first structured layer 340 of the photonic lattice, whose thicknessis typically in the range 0.02-10 μm, depending on the cutoff wavelengthof interest. For the 3D tungsten photonic crystal described herein, thethickness of the structured layer 340 can be 1.6 μm, and the initialthickness of silica layer 310 can be approximately 2.0 μm.

[0030]FIG. 3b shows the first silica layer 310 patterned to form aplurality of evenly spaced and parallel spacer bars 311 withapproximately rectangular cross-section. Such patterning can beaccomplished using a photolithographic etch mask (not shown) over silicalayer 310 with a plurality of openings in the etch mask at the locationswhere the material in layer 310 between the spacer bars 311 is to beremoved. An anisotropic etching process can then be used (e.g., reactiveion etching directed normal to the surface), resulting in bars 311having approximately rectangular cross-section. The etching step ispreferably performed to etch completely down through layer 310 to thesubstrate 300. The etch mask can then be stripped, resulting in thestructure of FIG. 3b. In the present example, the pitch between adjacentspacer bars 311 can be 4.2 μm and the width of the spacer bars can be3.0 μm.

[0031] In FIG. 3c, polysilicon 320 can be deposited by chemical vapordeposition to fill in the regions between the silica spacer bars 311.Again, the polysilicon thickness can be greater than the desired finalthickness of the first structured layer 340. Depositing the polysilicon320 generally leads to a complex and non-planar surface 321. Such arough and uneven surface could result in a poor quality photoniccrystal, due to scattering and uncontrolled reflections at the growthsurface. Therefore, chemical-mechanical-polishing (CMP) of the growthsurface is performed to planarize the growth surface prior to depositionof subsequent structural layers. CMP of the general type used in thepresent invention is disclosed in U.S. Pat. No. 5,998,298 to Fleming etal., which is incorporated herein by reference.

[0032] As shown in FIG. 3d, a first structured layer 340 comprising aplanar pattern of silica spacer bars 311 and polysilicon rods 341 isthereby produced. The polysilicon rods 341 are elongate, roughlyrectangular in cross section, and can be 1.2 μm wide and 1.6 μm thick.

[0033] As shown in FIG. 3e, repeating the same basic set of growth andprocessing steps, multiple structured layers 340 can be grown on top ofthe substrate 300 to form the desired photonic lattice structure 350with polysilicon. To form the Lincoln-Log structure, the orientation ofthe polysilicon rods 341 is rotated 90° between each structured layer340, and between every other layer the rods 341 are shifted relative toeach other by half of the pitch d. The structure 350 thereby has aface-centered-tetragonal lattice symmetry.

[0034] As shown in FIG. 3f, the polysilicon rods 341 can then be removedto form the lattice structure mold 360. The polysilicon rods 341 can beremoved using a 6M, 85° C. KOH etch, which has a selectivity of ˜100:1(Si to SiO₂). Over-etch during the KOH process, which is desirable toensure the removal of all the polysilicon 341, can result in theformation of a “V” structure 361 on the bottom of the layer 340contacting the silicon substrate 300. This is due to etching of theunderlying silicon substrate 300 and is dependent on the substratecrystallographic orientation. The KOH etch effectively stops when theetch-front encounters the slow etching (111) planes of the siliconsubstrate 300, thereby forming the “V” groove 361.

[0035] As shown in FIG. 3g, the lattice structure mold 360 can bebackfilled with a structural material. A variety of depositionprocesses, such as chemical vapor deposition (CVD), electroplating, orinfiltration with spin-on glasses or nanoparticles, can be used for thebackfilling of the mold 360, so long as the sacrificial material (e.g.,silica) can later be selectively removed from the backfilled structuralmaterial. For example, III-V compound semiconductors, II-VI materials,single and mixed oxides, nitrides, oxynitrides, metals, and metal alloyscan be deposited by CVD. A precursor conducting coating can be appliedto the lattice structure mold 360 and a wide variety of metals can beelectroplated from a solution to backfill the mold 360. Typicalelectroplated metals include copper, nickel, gold, iron, silver, cobalt,and chromium.

[0036] The lattice structure mold 360 can be backfilled with tungstenvia CVD to form tungsten rods 370 embedded in the silica mold material311. A precursor 50 nm thick TiN adhesion layer (not shown) can bedeposited on the mold 360 by reactive ion sputtering, since the blanketCVD tungsten film does not adhere to silicon dioxide. Tungsten can bedeposited at high pressure (e.g., 90 Torr) from WF₆ and H₂. The chemicalvapor deposition of tungsten results in films of very high purity. Thetungsten film can have a resistivity of 10 μOhm-cm. Backfilling of themold 360 with CVD tungsten 370 can result is a rough and uneven tungstengrowth surface 371 on the top surface of the mold 360.

[0037] As shown in FIG. 3h the top surface of the backfilled mold 360can planarized by CMP to remove the excess tungsten. A scanning electronmicrograph of a tungsten-backfilled, planarized mold 360 is shown inFIG. 4a. As shown in FIG. 4a, a keyhole 382 can be formed in the centerof the more deeply embedded lines of the tungsten rods 370, since thestep coverage of the CVD tungsten deposition process is not 100%.However, the film thickness is far greater than the skin depth oftungsten for electromagnetic radiation in the visible and infrared.

[0038] Finally, as shown in FIG. 3i, the silica spacer bars 311 can beremoved from the tungsten-backfilled and planarized lattice structuremold 360 by selective etching with a 1:1 HF-based solution. The resultis a 3D tungsten photonic crystal 380 comprising stacked tungsten rods370 on the silicon substrate 300. FIG. 4b shows a scanning electronmicrograph of the four-layer tungsten photonic crystal 380 comprisingthe stacked tungsten rods 370 on the silicon substrate 300. The tungstenphotonic crystal 380 has a stacking sequence that repeats itself everyfour layers, and has a face-center-tetragonal lattice symmetry. Thetungsten rod 370 width is 1.2 μm, rod-to-rod spacing is 4.2 μm and thefilling fraction of the high index tungsten is 28%. The tungstenphotonic crystal 380 retains sufficient structural integrity to behandled readily.

[0039] This fabrication process can be extended to create almost anyinterconnected photonic crystal having selective emissivity at visibleor infrared wavelengths. For example, current state-of-the-art siliconintegrated circuit processing tools are capable of shrinking the minimumfeature sizes to those required for structures that have photonicbandgaps in the near infrared and have selective emissivity in thevisible. See, e.g., “International Technology Roadmap forSemiconductors,” 1999 Edition [retrieved on 2001-08-09]. Retrieved fromthe Internet:<URL: http://public.itrs.net/files/1999_SIA_Roadmap/Home.htm>.

Optical Properties of the Tungsten Photonic Crystal

[0040] The optical properties of the 3D tungsten photonic crystal 380fabricated according to the above process were characterized using aFourier-transform infrared measurement system for wavelengths rangingfrom 1.5 to 25 μm. To obtain reflectance (R), a sample spectrum wastaken from a 3D tungsten photonic crystal 380 first and then normalizedto a reference spectrum of a uniform silver mirror. To find the absolutetransmittance (T), a transmission spectrum taken from a tungstenphotonic crystal 380 was normalized to that of a bare silicon wafer.This normalization procedure was to calibrate away extrinsic effects,such as light reflection at the air-silicon interface and absorption ofthe silicon substrate 300.

[0041]FIG. 5 shows the absolute reflectance spectrum 510 andtransmittance spectrum 520 of a four-layer tungsten photonic crystal380. The dashed line 530 shows the transmittance of a 6000 Å uniformtungsten film for reference. Light propagates along the <001> directionof the tungsten photonic crystal 380 and is unpolarized. The reflectance510 exhibits oscillations at λ<5.5 μm, raises sharply at λ˜6 μm (theband edge) and finally reaches a high reflectance of 90% for λ>8 μm.Correspondingly, the transmittance 520 shows distinct peaks at λ<5.5 μm,decreases sharply at λ˜6 μm (the band edge) and then vanishes to below1% for λ>8 μm. The simultaneous high R and low T at wavelengths greaterthan 8 μm indicates the existence of a photonic band gap in the tungstenphotonic crystal. The attenuation is ˜30 dB at λ=10 μm for thefour-layer tungsten photonic crystal 380, or equivalently a 7.5 dBattenuation per layer. The multiple oscillations at λ<5.5 μm areattributed to photonic density-of-states oscillations in the photonicallowed band.

[0042] As shown in FIG. 6, tilt-angle reflection spectra 600 were takento determine the angular dependence of the photonic band gap. Fortilt-angle transmission measurements, the tungsten photonic crystal 380was mounted on a rotational stage and the rotational angles spanned fromlight incident angles from 0° to 60°, measured from the surface normal(i.e., the <001> direction). The crystal orientation is tilted from the<001> to <110> axes. The light incident angle is thereforesystematically tilted away from G-X′ toward G-L of the first Brillouinzone. Four tilt-angle spectra 600 are shown in FIG. 6, for lightincident angles of 10, 30, 40, and 50°, respectively. As the lightincident angle is increased, the band edge position moves from λ˜6 μmfor q=10° to λ˜8 μm for q=50°. Both the oscillating features at λ<6 μmand the high reflectance at longer wavelength remain for all lightincident angles. Therefore, a large complete 3D photonic band gapexists, from λ˜8 μm to λ>20 μm, for the tungsten photonic crystal 380.

[0043]FIG. 7 shows the theoretical transmission spectra 700 for tungstenphotonic crystals of different number-of-layers, N=2, 4 and 6, plottedin a log-to-log scale. The dashed line 710 is a reference spectrum for auniform 6000 Å tungsten film. The theoretical transmission spectra 700were calculated according to the method of Sigalas et al. in Phys. Rev.B52, 11744 (1995). The transmittance 700 is very low in the bandgap(T<10⁻⁸ for N=6 layers), which is consistent with the small metallicskin-depth (300-500 Å for 1 μm<λ<25 μm), and is nearly independent ofwavelength. The crystal spectrum 700, on the other hand, exhibits a muchhigher transmission (T˜10⁻¹) in the allowed band, suggesting thatphotonic transport in the metallic allowed band is not dominated bymetallic attenuation. Moreover, a strong dependence on thenumber-of-layers of transmittance 700 is observed in the band gap (λ>8μm). This number-of-layers-dependence indicates that transmittanceattenuation at λ>8 μm scales with layer-thickness of the fabricatedstructure, but not the metallic skin depth. Hence, the observed lowtransmittance 700 is due primarily to the photonic band gap effect. Theattenuation constant in the band gap is extraordinarily large about 8,14 and 16 dB per layer at λ=10, 20 and 40 μm, respectively. Thissuggests that as few as four to six crystal layers are sufficient forachieving strong electromagnetic wave attenuation.

[0044] Such an extraordinarily large band gap is ideally suited forsuppressing broadband Blackbody radiation in the infrared and re-cyclingradiant energy into visible spectrum. FIG. 8 shows the spectralemissivity 800 of the tungsten photonic crystal 380. The crystal 380 hasa photonic bandgap (region with nearly zero emissivity) over a largerange in the far infrared (8 μm<λ<25 μm) portion of the spectrum. Thevery large photonic bandgap and large reduction in emissivity 800 in thefar infrared is due to the use of metal for the photonic crystal. In thephoton recycling process, the photonic band gap completely frustratesinfrared thermal emission and selectively forces the radiation intonear-infrared and visible emission. Consequently, energy is not wastedin heat generation, but rather re-channeled into a useful emission band.The lattice constant and refractory material of the photonic crystal canbe determined by the fabrication process. Therefore, the emission bandcan be tailored to be in the visible when the photonic crystal is heatedup to an elevated temperature of >1500° C., giving rise to a highlyefficient incandescent lamp.

[0045] It will be understood that the above description is merelyillustrative of the applications of the principles of the presentinvention, the scope of which is to be determined by the claims viewedin light of the specification. Other variants and modifications of theinvention will be apparent to those of skill in the art.

We claim:
 1. A photonically engineered incandescent emitter, comprisinga photonic crystal having a characteristic lattice constant andcomprising a refractory emitter material having a first dielectricconstant and at least one other lattice material having at least oneother dielectric constant and wherein the characteristic latticeconstant, the refractory emitter material, and the at least one otherlattice material are chosen so as to create a photonic bandgap thatmodifies thermal emission above a cutoff wavelength.
 2. The photonicallyengineered incandescent emitter of claim 1, wherein the at least oneother lattice material comprises air.
 3. The photonically engineeredincandescent emitter of claim 1, wherein the refractory emitter materialcomprises a metal.
 4. The photonically engineered incandescent emitterof claim 3, wherein the metal comprises tungsten or a tungsten alloy. 5.The photonically engineered incandescent emitter of claim 1, wherein therefractory emitter material comprises a non-metal.
 6. The photonicallyengineered incandescent emitter of claim 5, wherein the non-metalcomprises silicon carbide, carbon, or titania.
 7. The photonicallyengineered incandescent emitter of claim 1, wherein the characteristiclattice constant is less than 10 microns.
 7. The photonically engineeredincandescent emitter of claim 1, wherein the characteristic latticeconstant is less than 5 microns.
 8. The photonically engineeredincandescent emitter of claim 1, wherein the characteristic latticeconstant is less than 1 micron.
 9. The photonically engineeredincandescent emitter of claim 1, wherein the photonic crystal has acomplete bandgap.
 10. The photonically engineered incandescent emitterof claim 1, wherein the photonic crystal is two-dimensional.
 11. Thephotonically engineered incandescent emitter of claim 1, wherein thephotonic crystal is three-dimensional.
 12. A method for fabricating aphotonic crystal structure, comprising: a) forming a lattice structuremold of a sacrificial mold material on a substrate; b) depositing astructural material into the lattice structure mold; and c) removing thesacrificial material from the lattice structure mold to form thephotonic crystal.
 13. The method of claim 12, further comprisingpolishing the surface of the deposited emitter material prior to stepc).
 14. The method of claim 13, wherein the polishing ischemical-mechanical polishing.
 15. The method of claim 12, wherein theforming step a) comprises sequential deposition of a cavity-formingmaterial in alternating patterned layers of the sacrificial moldmaterial.
 16. The method of claim 12, wherein the depositing step b)comprises chemical vapor deposition, electroplating, or nanoparticleinfiltration.
 17. The method of claim 12, wherein the sacrificial moldmaterial comprises silica.
 18. The method of claim 12, wherein thesubstrate comprises silicon.
 19. The method of claim 15, wherein thecavity-forming material comprises polysilicon.
 20. The method of claim12, wherein the structural material is selected from the group ofmaterials consisting of III-V compound semiconductors, II-VIsemiconductors, single and mixed oxides, nitrides, oxynitrides, metals,and metal alloys.